In recent years, in the field of optical communications, large capacity optical transmission via a single optical fiber has been implemented by WDM (Wavelength Division Multiplexing) technology that performs transmission by multiplexing signals while allocating one signal to one wavelength. As this optical communication technology has been developed, attention has been drawn to optical switches for changing a signal path without converting an optical signal into an electric signal, etc. Among these switches, a wavelength selective switch that can select an arbitrary wavelength from several tens of wavelengths and output the wavelength to one of a plurality of output fibers (see, for example, patent literature 1) has been proposed. An example Wavelength Selective Switch (WSS) is illustrated in FIG. 1.
The wavelength selective switch in FIG. 1 includes a fiber array 001, a microlens array 002, a condenser lens 003, a cylindrical lens 004, a first main lens 005, a diffraction grating 006, a second main lens 007 and an MEMS mirror array 008, and has a configuration where these components are arranged in the order in the z direction.
The fiber array 001 is provided by arranging a plurality of optical fibers in the y direction, and is demultiplexed into an input port for emitting input light and an output port for receiving output light. In the example in FIG. 1, one input port 0011 and four output ports 0012 are provided. The microlens array 002 is arranged in the y direction in the same way as the fiber array 001, so that the individual microlenses are located opposite the corresponding optical fibers of the fiber array 001 on the output side of the input port and the input side of the output ports of the fiber array 001. The individual microlenses of the microlens array 002 shape beams that are emitted from the corresponding input and output ports of the optical fibers of the fiber array 001, and convert the beams into collimated rays.
The condenser lens 0003 concentrates light from the optical fibers to cross the principal rays at a specific point 009 (hereinafter referred to as a point A). A distance between the condenser lens 003 and the point A 009 is equal to the focal length of the condenser lens 003. The cylindrical lens 004 shapes the beam at the point A 009 into an elliptical form.
The first main lens 005, the second main lens 007 and the diffraction grating 006 constitute a 4 f optical system. The distance between the point A and the first main lens is equal to a focal length f1 of the first main lens, and the distance between the second main lens and the MEMS mirror is equal to a focal length f2 of the second main lens. Since the 4 f optical system is provided, the beam shaped at the point A 009 is projected to the MEMS mirror 008. The diameter of the beam projected to the MEMS mirror 008 is enlarged or reduced at a focal length ratio of f2/f1 relative to the beam diameter at the point A. The diffraction grating 006 serves to demultiplex, for each wavelength, signal light obtained by division multiplexing. The rays of the signal light demultiplexed for the individual wavelengths are emitted to the corresponding elements of the MEMS mirror through the second main lens 007.
The MEMS mirror 008 includes a plurality of mirror elements, which are aligned in the manner that the linear line that passes the centers of the individual mirror elements of the MEMS mirror 008 is extended in the x axial direction. The MEMS mirror 008 is arranged at the focal point of the second main lens in the state wherein the main faces of the individual mirror elements are located opposite the second main lens. The MEMS mirror 008 reflects, with an angle being changed to θx, the principal rays of the individual signal light that has been emitted, and selects output ports to which the rays enter. Since the individual mirror elements of the MEMS mirror 008 are rotated at the x axis that is perpendicular to the z axis for wavelength dispersion, the angle of incidence at the point A 009 is changed by changing the angle of emittance by the rotation. As a result, the wavelength selective switch can select the output port 0012 where the principal ray enters.
The wavelength selective switch can select the output port for each wavelength by changing the emittance angle for the MEMS mirror that is allocated for each signal light beam.
A plurality of these wavelength selective switches are mounted in a node 200 that is employed for an optical network. FIG. 2 is a structural diagram showing a wavelength selective switching unit where two wavelength selective switches (WSSes) are mounted on a single node. A wavelength selective switch 201 demultiplexes an optical signal received at the node 200 into a signal that is directed to the following wavelength selective switch 202 and a signal that is directed to receivers 203-1 and 203-2. The wavelength selective switch 202 at the succeeding stage multiplexes the signal received from the preceding wavelength selective switch 201 and the signal light received from transmitters 204-1 and 204-2, and outputs signal light from the node 200.
In the above described manner, for each node, the signals that are received and are to be transmitted, or passed through, can be demultiplexed and multiplexed by the wavelength selective switches. The node generally includes not only the wavelength selective switches, but also the other optical parts, such as an optical monitor, an optical amplifier and an optical coupler, and has functions, such as detection of a failure, compensation for the optical quality and detection of deterioration of the optical quality.
A configuration for a node employed when the number of routes is four is shown in FIG. 3. This node configuration can switch the individual signal wavelengths to arbitrary routes. At this time, eight wavelength selective switches are mounted. A case wherein the number of routes is four is employed for the description; however, an arbitrary number of routes can be employed, and as the number of routes is increased, the number of wavelength selective switches employed is also increased.
When multiple wavelength selective switches and optical parts are mounted to the node, the size of the node is increased, and the cost for the node is increased by the cost required for the number of components, such as the wavelength selective switches. Therefore, if common parts for a plurality of wavelength selective switches can be commonized and parts for which functional integration is available can be provided by using a single part, the sizes of the individual devices in the node can be reduced, and the cost can also be decreased.
In the present invention, the arrangement of input and output ports and the arrangement of an optical system, which are required for common use of parts, such as some optical parts included in a plurality of wavelength selective switches, are provided. Further, input/output port fabrication means for accurately mounting input and output ports, which will be increased by mounting a plurality of wavelength selective switches, is also provided. Furthermore, means for performing integration of the node function for the input and output ports of a wavelength selective switch is provided in order to reduce the sizes of the devices in the node.